Article for the 23 rd Sensing Forum

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Presented by:
Naoto Izumo 
R&D Division, A&D Company, Limited 
October 2 ~ 3, 2006 
Tsukuba Center Inc. 
Tsukuba, JAPAN

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Physical Quantity Measured by a Vibration Viscometer 
Subtitle: The JCSS Standardization of Viscosity 
Naoto Izumo 
R&D Division, A&D Co., Ltd. 
Higashi-Ikebukuro, Toshima-ku, Tokyo 170-0013 Japan 
Abstract 
The objective of this article is to introduce a viscometer that utilizes a new viscosimetry 
measuring method. In addition, the article will recommend a new unit system, which is 
utilized in the vibration viscometer. Using examples, the article explains JCSS viscosity 
standardization and recent requirements for viscosity measurements.
Keywords: 
Vibration Viscometer, Static Viscosity (Viscosity × Density), Viscosity 
JCSS, Cloud Point 
Introduction 
The following is an introduction of the vibration viscometer, a new method for 
measuring viscosity. In addition to providing a description of the physical quantity that 
is measured using the vibration viscometer, a new unit system for viscosity will be 
proposed. Furthermore, there is an explanation regarding the Japan Calibration 
Service System (JCSS) standardization of viscosity and viscosity measurements using 
actual examples. There is also discussion of recent requirements for measuring 
viscosity. 
History and Development of Viscosity Measurement 
The history of viscosity measurements is extensive and is believed to date back to when 
people began measuring the viscosities of engine oils with the advent of the automobile 
industry in the United States. In the U.S., it had become necessary to control the 
viscosities of engine oils as a method of maintaining the performance of engines. Even 
today, viscosities of engine oils are standardized for both high and low temperatures, 
such as 5W-30.
It is believed that if the viscosity of oil reaches below 2.6 cp (the viscosity 
of purified water at 20
˚
C is approximately 1 cp = 1 mPa
·
s : 1 milliPascal second) the 
engine will burn out.
This has recently become an important issue when developing 
energy-saving engine oils for the purpose of improving fuel efficiency. Furthermore, the 
demand for viscosity measurements aimed at maintaining quality in the field of 
cutting-edge technologies has been increasing. This is due in part to the expansion of 
new markets for viscosity-related applications, which now include resist inks for liquid 

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crystals, abrasives for semi-conductors, glass coating materials, powder particle size 
distribution, polymeric emulsion and cloud point measurement of surface-active agents. 
Moreover, recently there have been discussions of performing viscosity measurements of 
human blood. Studies have shown that high blood viscosity increases the possibility of 
sudden death due to diseases affecting the circulatory system. The viscosity of human 
blood, although dependent on the measurement method, is generally believed to fall 
somewhere between approximately 3 and 10 mPa
·
s. 
Actual examples of the measurements of the viscosity and temperature of engine oil and 
cloud point measurements of nonionic surface-active agents have been presented in 
Figures 1 and 2 for reference. 
Definition of Viscosity and the JCSS Standardization 
Viscosity is defined using the relative motion between two boards that have been placed 
opposite to each other in a sample liquid. Viscosity is the proportional constant when 
the interactive force (shear stress) per unit area generated in the planar direction 
between the opposing two boards, and the velocity gradient (shear rate), calculated by 
dividing the relative displacement speed by the distance between the two boards, are 
proportional. Based on this definition, there is a proportional relationship between the 
shear stress and the shear rate. The fluid is called a Newtonian fluid in the event that 
the shear stress and the shear rate are proportional, and viscosity is indicated as a 
constant stable value. On the other hand, if the proportional relationship with the shear 
Viscosity change of gasoline engine oil 
Cloud point measurement 
Figure 1. 
Figure 2. 

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stress deteriorates due to changes in the shear rate or if the proportional relationship is 
lost due to temporal changes (a fixed viscosity value cannot be determined for the liquid 
due to the measurement conditions), all such fluids are collectively called 
non-Newtonian fluids. While as demonstrated above, it is easy to define viscosity, the 
structures of the devices to conduct actual measurements are not as simple and there 
are many structural problems. For example, it is important to stabilize the measuring 
environments, such as keeping the measuring temperature constant, for methods like 
the cup type, which measures the time taken by the sample liquid to flow from the 
opening of a given sample cup, the falling-sphere type, which measures the viscosity by 
the time needed for a rigid body to fall within the sample liquid, and the capillary type, 
which measures the time taken by the sample liquid to flow inside a capillary. For the 
rotation type, it is necessary to regulate the rotation of a rotor at a constant speed and 
steadily measure the torque required for the rotation. On the other hand, for the 
vibration type, which calculates the viscosity from the power to drive an oscillator 
placed in a sample liquid, technology to steadily vibrate the oscillator at the natural 
frequency is essential. Among viscosity measurements based on the measurement 
principles above, the underlying theory of the measurement principle that has become 
the modeling formula (modeling equation) and the “uncertainties” inherent in the 
measurements have been demonstrated with the capillary, rotation and vibration types.
As a result, along with the standard liquids of viscosity, these types of viscometers were 
accredited as the JCSS standard devices and have been uploaded to the official website 
of the National Institute of Technology and Evaluation (NITE) as of April 2006. 
Physical Quantity Measured by Each Measurement Method 
Next is a brief explanation of the measurement principles for viscosity standardized by 
the JCSS: 
Capillary type: A liquid filling a given vessel is made to flow to a lower position by 
gravity and the viscous behavior of the liquid is measured based on the flow time. The 
time taken by the liquid for the movement is measured and is converted to a viscosity 
value using the flow time of internationally standardized water as a reference. When 
using this measurement principle, the physical quantity to be measured (i.e. time) is 
proportional to the viscosity, but inversely proportional
to density. Therefore, this 
physical quantity can be expressed as “viscosity/density,” and is called the “kinetic 
viscosity.” 
Rotation type: A rotor is placed in a liquid and is constantly rotated. During rotation, 

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the torque necessary for the rotation is proportional to the viscosity. The “viscosity” is 
the physical quantity that is measured. 
Vibration type: An oscillator placed in a liquid is vibrated at a constant displacement 
magnitude. By detecting the power necessary for the vibration, the viscous behavior of 
the liquid is measured. The physical quantity to be measured is expressed as “viscosity 
× density.” 
Advantages and Measurement Principles of the Vibration Viscometers
There are two kinds of vibration viscometers,
the rotational vibration type and the 
tuning-fork vibration type – both types rely on the same measurement principle.
The 
present section is devoted to a detailed explanation of the tuning fork vibration method. 
A viscometer using the tuning-fork method has a pair of opposing oscillators of the same 
natural frequency. Each of these oscillators is individually synchronized and driven by 
electromagnetic power. As the two oscillators move in opposite phases, no outward 
reactive force is generated: this is true with a tuning fork. Driving at a natural 
frequency with very small damping is also possible. During the viscosity measurement, 
the amplitude that is generated is constantly measured and controlled in order to 
maintain a fixed amplitude. In addition, the electromagnetic power required to drive 
the oscillators is also measured. Viscosity is determined based on variations in driving 
power in accordance with viscosity multiplied by the density of the liquid in which the 
oscillators are immersed. The energy applied to the sample liquid is small because the 
vibration method causes only minute displacement in the sample liquid. Moreover, as 
the thermal capacity of the oscillator is small, interference to the sample substance due 
to the measurement can be minimized. Since there is no flowing or churning of the 
sample liquid, little change is caused mechanically to the physical properties of the 
sample even after the measurement starts, making a speedy and stable measurement 
possible. The viscosity of a liquid is temperature dependent and varies by as much as –2 
~ –10%/
˚
C. Hence, small interference by the measuring system can provide benefits 
such as decreasing the possibility of temperature variation that can cause changes to 
the physical properties of the sample. In addition, by utilizing a tuning-fork vibration, 
the viscometer has a high measurement sensitivity and is capable of performing 
continuous measurements, ranging from as low as 0.3 mPa
·
s (1/3 the viscosity of 
purified water) to 10,000 mPa
·
s. This enables the measurement of the cure processes of 
materials such as adhesives, gelatin, and egg albumen. For example, the cure processes 
of albumen proteins with different constituents can be monitored at different 
temperatures. The physical quantity measured by the vibration viscometer is, from the 

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theoretical formula, “viscosity × density” in principle. 
Next, is an explanation of the measurement model for the tuning-fork vibration 
viscometers. As illustrated in the model of the free vibration system shown in Figure 3, 
inertia terms based on the mass of the measuring system, viscous terms based on the 
viscosity of the liquid, and the spring terms based on the spring constant of the 
measuring system can be examined.
When the measuring system is driven by 
electromagnetic power at the natural frequency determined by the mass and spring 
constant of the measuring system, the inertial force and the restorative force of the 
spring will balance each other, and the energy consumed by the measuring system will 
only be the viscous term of the liquid. This information is presented in Formula (1) 
expressed as a motion equation, where F: Excitation force, m: Mass, C: Viscosity 
coefficient, K: Spring constant, x: Amplitude, 
ω
n: Natural frequency of the vibration 
system